A large portion of US households (60%) have at least one family member that suffers from hypersensitive teeth. Products, such as toothpaste, targeting consumers suffering from tooth sensitivity are the fastest growing segment of the oral care market; however, the results provided by sensitivity toothpastes leave a majority of users (60%) unsatisfied, with 57% of sufferers willing to try products other than toothpaste.
Tooth sensitivity can be activated by hot and cold drinks and certain acidic or hypertonic foods. This sensitivity often occurs when gum tissue recedes from the necks of teeth, exposing root surfaces that are not covered by hard enamel but by soft cementum. The cementum is so thin and soft that it can be removed by tooth brushing, thereby exposing the sensitive underlying dentin. The dentin can also become exposed under restorations. The pain that patients feel from exposed dentin is called dentin sensitivity, as reported in Pashley, Arch Oral Biol 39 (Suppl) 735-805 (1994).
Dentin sensitivity, whether on exposed surfaces at the necks of teeth or under restorations, is reportedly due to minute fluid shifts across dentin in response to painful stimuli (Brannstrom, Oper Dent 9: 59-68, 1984). This theory, called the hydrodynamic theory, (Brannstrom and Astrom, Int Dent J 22: 219-j226, 1972), assumes that fluid can move within or through the microscopic tubules making up dentin, at a rate that activates mechanoreceptor nerves in the dentin pulp. When the surface of the tooth is eroded, the dentinal tubules become exposed to the external environment. The exposed dentinal tubules provide a pathway for transmission of fluid flow to the pulpal nerves and this is induced by changes in temperature, pressure and ionic gradients. By blocking the tubules, the external stimuli have a diminished effect, and less pain will be felt. A number of agents have been previously screened for their ability to occlude dentinal tubules, including potassium oxalate (Greenhill and Pashley, J Dent Res 60: 686-698, 1981).
Hypersensitive teeth can cause pain and discomfort when subjected to changes in temperature, pressure, or chemical action. Exposure of the dentin frequently leads to hypersensitivity. Dentin exposure may occur due to recession of the gums, periodontal disease and improper dental care.
Hypersensitive teeth are commonly treated with a nerve desensitizer such as potassium nitrate or potassium chloride. Alternatively, hypersensitive teeth may also be treated with an ingredient intended to occlude the tubuli, such as strontium acetate, strontrium chloride, stannous fluoride, ferric oxalate or potassium oxalate. Application of the therapeutic ingredient may be via a non-prescription preparation, such as a dentifrice or rinse, or via products professionally applied or prescribed.
There have been various in vitro methods that have been developed to measure the effectiveness of various treatments and compositions to treat dentin so that it's less permeable. An effective method should reproduce the microenvironment in and around the tubule orifice, provide the correct geometry, appropriate surface chemistry, and relevant fluid composition and movement. One method was developed by Pashley (J. Periodontology, vol. 55, no. 9, pg. 522, September 1984). Pashley utilizes sectioned dentin discs of predetermined thickness which are placed between two o-rings within a two part chamber. Positive pressure is used to drive a testing fluid through the bottom chamber to the dentin section; the amount of fluid passing through the dentin is then measure to determine hydraulic conductance. The system was used to measure the effect of any desensitizing toothpastes had on reducing the permeability of the dentin.
One of the issues with the Pashley device has been with visualization. The upper portion of the device is usually covered so direct visualization of fluid moving through dentin is not possible. Further, as the dentin is covered by the top portion of the device in order to treat the dentin, for example by brushing with toothpaste or application of a tooth whitening strip) after a baseline measurement has been taken the top portion must be removed and then reattached, which could damage the dentin and/or alter the results.
Therefore, what is needed is a device allowing for direct manipulation of a dentin section while the dentin section is secured within the testing device, and which allows the dentin section to be visible during testing.